1. Field of the Invention
The present invention relates to a method for transmitting data, an apparatus for recording data, a record (recording, recordable or recorded) medium, and an apparatus for reproducing data all of which are suitable to preventing illegal copying or incorrect use or applicable to a charging system.
2. Description of the Related Art
In recent days, with increase of capacity and prevalence of a digital record medium like an optical disk, great significance has been placed on preventing illegal copying and inhibiting incorrect use of such a medium. The digital audio data or the digital video data can be easily copied into a complete duplication with no degradation. The computer data can be also more easily reproduced. Illegal copying of data takes place in the market.
To prevent illegal copying of digital audio data or digital video data, the so-called SCMS (Serial Copy Management System) or CGMS (Copy Generation Management System) standards have been known. These standards are arranged so that a copy prohibitive flag is set to a specific portion of the recorded data. Even with these standards, the data may be extracted by a method such as a dump copy.
As disclosed in Japanese Laid-open No.Showa 60-116030, another method has been proposed for encrypting a content of a computer data file and granting the encrypted content to registered users only. This method is concerned with the system arranged to take the steps of distributing a digital record medium on which the encrypted data is recorded or making the encrypted digital data accessible to any user through a wired or wireless transmission path as a distributing format of data and providing the users having paid a fee for the key data for the necessary data so that these users may decode the encrypted digital data and use the data. It is thus desirable to establish the simple and useful encryption.
The present invention is made in consideration of the aforementioned circumstances. It is an object of the present invention to provide a method for transmitting data, an apparatus for recording data, a record (recording, recordable or recorded) medium, and an apparatus for reproducing data that are arranged so that the data may be encrypted with simple composition but only the registered users can access key data for the encrypted data.
To solve the foregoing problems, the present invention is characterized to transmit or record information data containing parity data by converting all or part of the information data handled in doing error correction or error detection coding for input digital data, and all or part of the information data obtained without doing the data conversion. The data conversion contains a logic operation, an inversion, or a replacement of the information data according to key information or data for encryption.
A medium for recording data according to an aspect of the invention is characterized to record the parity data and the information data.
A method for reproducing data according to an aspect of the invention is characterized to perform data conversion with respect to at least part of data treated in the process of error correction or error detection coding according to the key information for encryption and then perform data conversion with respect to the data according to the key information for encryption contained in the data treated in the process of the error correction or error detection decoding corresponding to the above process.
In operation, the data reproducing method is arranged to transmit or record on the record (recording, recordable or recorded) medium information data containing parity data obtained by converting the information data treated in the process of error correction or error detection coding based on the key information or key data and all or part of the information data that is not converted. The key information concerns with only he parity data or part of the information data. The key information cannot be detected from these data.
According to the present invention, the information data treated in the process or error correction coding or error detection coding is converted according to the key information for encryption for generating a parity. The operation is executed to output the information data containing this parity data and all or part of the information data before conversion. Hence, no key information is leaked out of the output data, so that the encryption may be done by using the key information with high secrecy.
Further, in the process of error correction coding, the key can be encrypted with a great number of bits. The encryption is realized in a huge black box such as an error correction coding or decoding IC or LSI. This makes it quite difficult for the ordinary persons to decode the encrypted data, thereby greatly improving the data security.